As a conventional art for manufacturing a machined part, as shown in FIG. 6, a machined part 100′ is generally manufactured by hot-forging a raw material 100 (S12), cold-forging this raw material 100 to introduce a dislocation into an entirety thereof and form a graphite deposition nucleus (S13), performing a graphitization treatment for depositing graphite over the entire raw material 100 by maintaining a state of being heated to a predetermined temperature for a predetermined time (S14), then machining a predetermined region 100a, such as molding a gear etc. through the formation of a tooth space by, for example, cutting or the like (S15), and heating this region to the predetermined temperature for the predetermined time to solidly re-dissolve graphite (S16). A material that allows graphite to be deposited through the graphitization treatment is preferred as a raw material for manufacturing this machined part 100′. By depositing graphite through the graphitization treatment, the concentration of carbon in the raw material becomes relatively low. Therefore, the machinability at the time of machining can be enhanced.
Besides, as another conventional art, Patent Document 1 is known. Patent Document 1 relates to a steel product for a mechanical structure that is excellent in cold workability, and to a method for manufacturing the steel product. Patent Document 1 discloses performing cold working with a suitable reduction of area after hot working, splitting layers of cementite, introducing a strained dislocation as a deposition nucleus of graphite, and homogeneously, finely and swiftly depositing graphite through a subsequent annealing treatment, etc. (0025).